Surface inspecting apparatus and surface inspecting method

ABSTRACT

There is provided a surface inspecting apparatus capable of performing inspection at higher speed and with higher accuracy. A surface inspecting apparatus ( 1 ) is provided with an illumination optical system ( 30 ) for irradiating linearly polarized light to a surface of a wafer ( 10 ) under a plurality of inspection conditions; an imaging optical system ( 40 ) for capturing an image of the wafer ( 10 ) formed by polarization components having an oscillation direction that is different from that of the linearly polarized light as part of reflected light from the surface of the wafer ( 10 ) irradiated by the linearly polarized light under the plurality of inspection conditions; and an image-processing apparatus ( 50 ) for extracting for individual pixels an image having the smallest signal intensity from among images of the wafer ( 10 ) captured under the plurality of inspection conditions by the imaging optical system ( 40 ), and for inspecting for the presence of defects in a repeated pattern of the wafer ( 10 ) on the basis of an inspection image of the wafer ( 10 ) generated by connecting each of the extracted pixels.

This is a continuation of PCT International Application No.PCT/JP2009/051962, filed on Feb. 5, 2009, which is hereby incorporatedby reference. This application also claims the benefit of JapanesePatent Application No. 2008-026759, filed in Japan on Feb. 6, 2008,which is hereby incorporated by reference.

TECHNICAL FIELD

The present invention relates to a surface inspecting apparatus andsurface inspecting method for inspecting the surface of a semiconductorwafer, liquid crystal substrate, or the like.

TECHNICAL BACKGROUND

In the process of manufacturing a semiconductor circuit element orliquid crystal display element, repeated patterns (wiring patterns andother line-and-space patterns) formed on the surface of thesemiconductor wafer or liquid crystal substrate (hereinafter referred togenerically as “the substrate”) are inspected for defects. In anautomated surface inspecting apparatus, the substrate is placed on atiltable stage, illuminating light (non-polarized light) for used inperforming an inspection is irradiated onto the surface of thesubstrate, an image of the substrate is acquired based on diffractedlight (e.g., 1^(st)-order diffracted light) generated from the repeatedpattern on the substrate, and the locations of defects in the repeatedpattern are identified based on the differences between lightness anddarkness (contrast) in the image (see, e.g., Patent Document 1). In sucha surface inspecting apparatus, adjusting the tilt of the stage makes itpossible to inspect for defects in a repeated pattern having a differentrepetition pitch on the substrate.

Techniques for inspecting a repeated pattern formed on the surface of asubstrate include inspection using diffracted light such as describedabove (referred to hereinafter as diffraction inspection), using directreflection light, utilizing changes in polarization state due tostructural birefringence of the pattern (hereinafter referred to as PERinspection), and other techniques. These inspection methods enableresist application defects, line width defects based on defocusing ordose shift of an exposure apparatus, and other defects to be detected athigh speed with high accuracy.

As the line width of the repeated pattern decreases, the wavelength ofthe illumination used for diffraction inspection must be shortened, andin repeated patterns having a line width of 45 nm or less, there is noillumination light source that is optimal for diffraction inspection,and the inspection is performed by PER inspection. In repeated patternshaving a line width of 45 nm or less, changes in the shape of thepattern on the order of 1 nm must be detected, and high sensitivity isrequired to detect changes in the shape of the pattern.

Patent Document 1: Japanese Laid-open Patent Publication No. H10-232122

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

Although three types of parameters such as the illumination wavelength,for example, are known as conditions that enhance the sensitivity ofdetection in PER inspection, it is difficult to derive the optimuminspection conditions by combining these three types of parameters, andthere is also no method of determining the appropriateness of inspectionconditions. Performing all inspections under a plurality of inspectionconditions with varying parameters is also problematic because of thelong time required, and false positives occur in defect detection.

The present invention was developed in view of such problems, and anobject of the present invention is to provide a surface inspectionapparatus and surface inspection method capable of inspection at highspeed with high accuracy.

Means to Solve the Problems

The surface inspection apparatus of the present invention for achievingthe abovementioned objects comprises an illumination unit forirradiating linearly polarized light onto a surface of an inspectedsubstrate having a predetermined repeating pattern; an imaging unit forcapturing an image of the inspected substrate formed by polarizationcomponents having an oscillation direction that is different from thatof the linearly polarized light as part of the reflected light from thesurface of the inspected substrate irradiated by the linearly polarizedlight; a setting unit for setting a plurality of conditions in at leastone of an illumination condition in the illumination unit and an imagingcondition in the imaging unit; and an information processing unit forcalculating a signal intensity for each portion of each of a pluralityof images of the inspected substrate photographed by the imaging unitunder the plurality of inspection conditions, comparing the signalintensity of the same portions in the plurality of images of theinspected substrate, and generating inspection information of theinspected substrate from information of the portions having the smallestsignal intensity.

In the surface inspection apparatus described above, the signalintensity is preferably a signal intensity standardized according to thesignal intensity from a normal repeating pattern.

The surface inspection apparatus described above preferably comprises adisplay unit for generating an inspection image on the basis of theinspection information generated by the information processing unit andvisibly displaying the inspection image.

The surface inspection apparatus described above preferably comprises aninspection unit for inspecting for the presence of a defect in therepeating pattern; wherein the inspection unit is configured so as toinspect for the presence of a defect in the repeating pattern bycomparing the inspection information and predetermined referenceinformation; the illumination unit irradiates linearly polarized lightto a surface of a reference substrate as a reference for the inspectionunder the plurality of inspection conditions, and the imaging unitcaptures an image of the reference substrate formed by polarizationcomponents having an oscillation direction that is different from thatof the linearly polarized light as part of the reflected light from thesurface of the reference substrate irradiated by the linearly polarizedlight; and the information processing unit calculates a signal intensityfor each portion of each of the plurality of images of the referencesubstrate photographed by the imaging unit under the plurality ofinspection conditions, compares the signal intensity of the sameportions in the plurality of images of the reference substrate, extractsa portion having the smallest signal intensity for each of the portions,and generates the reference information from information of theextracted portion.

In the surface inspection apparatus described above, the inspectioncondition set by the setting unit is preferably an angle formed by theoscillation direction of the linearly polarized light and theoscillation direction of the polarization components.

In the surface inspection apparatus described above, the inspectioncondition set by the setting unit is preferably an angle formed by therepetition direction of the repeating pattern and the oscillationdirection of the linearly polarized light on the surface of theinspected substrate.

In the surface inspection apparatus described above, the inspectioncondition set by the setting unit is preferably the wavelength of thelinearly polarized light.

The surface inspection method of the present invention comprises a firststep of setting an inspection condition; a second step of irradiatinglinearly polarized light onto a surface of an inspected substrate havinga predetermined repeating pattern; a third step of capturing an image ofthe inspected substrate formed by polarization components having anoscillation direction that is different from that of the linearlypolarized light as part of the reflected light from the surface of theinspected substrate irradiated by the linearly polarized light; and afourth step of calculating a signal intensity for each portion of eachof a plurality of images of the inspected substrate photographed underthe plurality of inspection conditions in the third step, comparing thesignal intensity of the same portions in the plurality of images of theinspected substrate, and generating inspection information of theinspected substrate from information of the portions having the smallestsignal intensity.

The surface inspection method described above preferably comprises afifth step of generating an inspection image on the basis of theinspection information generated in the fourth step and visiblydisplaying the inspection image.

The surface inspection method described above preferably comprises asixth step of inspecting for the presence of a defect in the repeatingpattern on the basis of the inspection information generated in thefourth step, the sixth step comprising inspecting for the presence of adefect in the repeating pattern by comparing the inspection informationand predetermined reference information; a seventh step of irradiatinglinearly polarized light onto a surface of a reference substrate as areference for the inspection under the plurality of inspectionconditions; an eighth step of capturing an image of the referencesubstrate formed by polarization components having an oscillationdirection that is different from that of the linearly polarized light aspart of the reflected light from the surface of the reference substrateirradiated by the linearly polarized light under the plurality ofinspection conditions; and a ninth step of calculating a signalintensity for each portion of each of the plurality of images of thereference substrate photographed under the plurality of inspectionconditions in the eighth step, comparing the signal intensity of thesame portions in the plurality of images of the reference substrate toextract the portions having the smallest signal intensity for each ofthe portions, and generating the reference information from informationof the extracted portions.

In the surface inspection method described above, the inspectioncondition set in the first step is preferably an angle formed by theoscillation direction of the linearly polarized light and theoscillation direction of the polarization components.

In the surface inspection method described above, the inspectioncondition set in the first step is preferabl_(y) an angle formed by therepetition direction of the repeating pattern and the oscillationdirection of the linearly polarized light on the surface of theinspected substrate.

In the surface inspection method described above, the inspectioncondition set in the first step is preferably the wavelength of thelinearly polarized light.

ADVANTAGEOUS EFFECTS OF THE INVENTION

The present invention enables inspection at higher speed and accuracy.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing the overall structure of the surface inspectionapparatus according to the present invention;

FIG. 2 is a view showing the appearance of the surface of thesemiconductor wafer;

FIG. 3 is a perspective view showing the irregular structure of therepeating pattern;

FIG. 4 is a view showing the state of inclination between the plane ofincidence of the linearly polarized light and the repetition directionof the repeating pattern;

FIG. 5 is a schematic view showing the illumination apparatus;

FIG. 6 is a first flowchart showing the surface inspection methodaccording to the present invention;

FIG. 7 is a second flowchart showing the surface inspection methodaccording to the present invention; and

FIG. 8 is a view showing a modification of the surface inspectionapparatus.

EXPLANATION OF NUMERALS AND CHARACTERS

-   -   1: surface inspection apparatus    -   10: wafer (inspected substrate)    -   12: repeated pattern    -   30: illumination optical system (illumination unit)    -   40: imaging optical system (imaging unit)    -   50: image-processing apparatus (image processing unit, display        unit, and inspection unit)    -   55: control apparatus (setting unit)    -   L: linearly polarized light

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will be described withreference to the drawings. As shown in FIG. 1, the surface inspectionapparatus 1 according to the present embodiment is composed primarily ofa stage 20 for supporting a semiconductor wafer 10 (hereinafterabbreviated as wafer 10) as the substrate under inspection, anillumination optical system 30, an imaging optical system 40, animage-processing apparatus 50, and a control apparatus 55. The surfaceinspection apparatus 1 is an apparatus for automatically inspecting asurface of the wafer 10 in the process of manufacturing a semiconductorcircuit element. The wafer 10 is transported from a wafer set ordevelopment apparatus (not shown in the drawing) by a conveyance system(not shown in the drawing) after exposure/development of a resist filmforming the topmost layer, and the wafer 10 is retained on the stage 20by suction.

On the surface of the wafer 10, a plurality of chip regions 11 isarranged in the X and Y directions, and a predetermined repeatingpattern 12 is formed in each of the chip regions, as shown in FIG. 2. Asshown in FIG. 3, the repeating pattern 12 is, e.g., a resist pattern(e.g., wiring pattern), in which a plurality of line portions 2A isarranged at a constant pitch P in the minor-axis direction (X direction)thereof. Space portions 2B occur between adjacent line portions 2A. Thearrangement direction (X direction) of the line portions 2A is referredto as the “repetition direction of the repeating pattern 12.”

Here, the line width D_(A) of the line portions 2A in the repeatingpattern 12 is set to a value ½ the pitch P. Specifically, the repeatingpattern 12 has an irregular shape in which line portions 2A and spaceportions 2B are alternately arranged in the X direction, and whenexposed at the proper exposure focus, the pattern edges are sharplyformed. In the case of such an ideal shape, the luminance (signalintensity) of the polarization components detected by the imagingoptical system 40 described hereinafter is maximized. However, when theexposure focus is not at the proper value, pattern breakdown occurs, andthe luminance of the polarization components at this time is reducedrelative to the ideal case.

The surface inspection apparatus 1 of the present embodiment performsdefect inspection (PER inspection) of the repeating pattern 12 byutilizing luminance variations (variations in signal intensity) in therepeating pattern 12 such as described above, i.e., variations in thepolarization state due to structural birefringence of the pattern. Asdescribed above, luminance variations are caused by a discrepancy of theexposure focus from the proper state, and occur in each shot region ofthe wafer 10.

In the present embodiment, the pitch P of the repeating pattern 12 isset adequately small in relation to the wavelength of the illuminatinglight (linearly polarized light described hereinafter) directed to therepeating pattern 12. Diffracted light from the repeating pattern 12 istherefore not created, and cannot be used to inspect the repeatingpattern 12 for defects.

The stage 20 of the surface inspection apparatus 1 supports the wafer 10on the top surface thereof, and fixes the wafer 10 in place, e.g., byvacuum suction. The stage 20 is also capable of rotating about a normalA1 as a rotational axis in the center of the top surface of the stage.This rotation mechanism enables the repetition direction (X direction inFIGS. 2 and 3) of the repeating pattern 12 in the wafer 10 to be rotatedon the surface of the wafer 10.

In the present embodiment, in order to maximize the reflectance ofdefect inspection for the repeating pattern 12, the repetition directionof the repeating pattern 12 in the wafer 10 is set to an angle of 45°with respect to the oscillation direction of the illuminating light(linearly polarized light L) on the surface of the wafer 10. This angleis not limited to 45°, and may be set to 22.5°, 67.5°, or any otherangle direction.

As shown in FIG. 1, the illumination optical system 30 is composed of anillumination apparatus 60 for emitting light at a specific wavelength, afirst polarizing plate 32, and a first lens 33. As shown in FIG. 5, theillumination apparatus 60 is composed of three illuminators 61 a, 61 b,61 c for emitting light having mutually different wavelengths, and acollecting optical system 63 for directing the light emitted from eachof the illuminators 61 a, 61 b, 61 c to the wafer 10. The firstilluminator 61 a is not shown in detail in the drawings, but is composedof a xenon lamp, mercury lamp, or other light source; an interferencefilter (band-pass filter) for extracting a desired wavelength component(bright-line spectrum) from the light from the light source, and othercomponents, and the first illuminator 61 a is configured so as to emitlight having a wavelength of 546 nm (e-line).

The second illuminator 61 b has the same structure as the firstilluminator 61 a, but is configured so as to emit light having awavelength of 436 nm (g-line). The third illuminator 61 c also has thesame structure as the first illuminator 61 a, but is configured so as toemit light having a wavelength of 405 nm (h-line). The threeilluminators 61 a, 61 b, 61 c each actually emit light in wavelengthregions ±10 nm to ±30 nm from the aforementioned wavelengths.

The collecting optical system 63 is composed of three collective lenses64 a, 64 b, 64 c, three neutral density filters 65 a, 65 b, 65 c, andthree mirrors 66, 67, 68. The first collective lens 64 a collects thelight emitted from the first illuminator 61 a and directs the light tothe first neutral density filter 65 a. The second and third collectivelenses 64 b, 64 c collect the light emitted from the second and thirdilluminators 61 b, 61 c, respectively, and direct the light to thesecond and third neutral density filters 65 b, 65 c, in the same manneras the first collective lens 64 a.

The first neutral density filter 65 a is formed having a disk shape inwhich the transmittance continuously varies in the circumferentialdirection, and the light from the first collective lens 64 a istransmitted by the first neutral density filter 65 a to the first mirror66. The first neutral density filter 65 a is configured so as to berotatable in the circumferential direction by a rotary drive apparatusnot shown in the drawing, and the quantity of light emitted from thefirst illuminator 61 a is adjusted in accordance with the rotation angleof the first neutral density filter 65 a. The second and third neutraldensity filters 65 b, 65 c also have the same structure as the firstneutral density filter 65 a, and the light from the second and thirdcollective lenses 64 b, 64 c is transmitted by the second and thirdneutral density filters 65 b, 65 c, respectively, to the second andthird mirror 67, 68. The quantity of light emitted from the second andthird illuminators 61 b, 61 c is also adjusted in accordance with therotation angle of the second and third neutral density filters 65 b, 65c, respectively.

A first shutter 69 a is provided between the first neutral densityfilter 65 a and the first mirror 66 so as to be insertable into andremovable from the optical path, and is configured so that illuminationby the first illuminator 61 a can be switched on and off. A secondshutter 69 b is provided between the second neutral density filter 65 band the second mirror 67 so as to be insertable into and removable fromthe optical path, and is configured so that illumination by the secondilluminator 61 b can be switched on and off. A third shutter 69 c isprovided between the third neutral density filter 65 c and the thirdmirror 68 so as to be insertable into and removable from the opticalpath, and is configured so that illumination by the third illuminator 61c can be switched on and off.

The third mirror 68 is a normal reflective mirror. The light from thethird neutral density filter 65 c is reflected toward the second mirror67 by the third mirror 68. The second mirror 67 is a so-called dichroicmirror. The light from the second neutral density filter 65 b isreflected toward the first mirror 66 by the second mirror 67, and thelight from the third neutral density filter 65 c is transmitted by thesecond mirror 67 toward the first mirror 66.

The first mirror 66 is also a so-called dichroic mirror. The light fromthe first neutral density filter 65 a is transmitted by the first mirror66 toward the surface of the wafer 10, and the light from the secondmirror 67 is reflected by the first mirror 66 toward the surface of thewafer 10. Through this configuration, by opening any one of the firstthrough third shutters 69 a through 69 c, any one of the beams from thefirst through third illuminators 61 a through 61 c (i.e., light having awavelength of 546 nm (e-line), 436 nm (g-line) or 405 nm (h-line)) canbe selectively emitted toward the wafer 10. By opening a plurality ofshutters, the light from (any of) the first through third illuminators61 a through 61 c can be synthesized and emitted to the wafer 10.

The first polarizing plate 32 is disposed on the optical path betweenthe illumination apparatus 60 and the first lens 33, and converts thelight emitted from the illumination apparatus 60 into linearly polarizedlight L (see FIG. 4) in accordance with the orientation of thetransmission axis thereof. The first lens 33 converts the illuminationlight from the first polarizing plate 32 to a parallel luminous fluxwhich is irradiated to the wafer 10 that is the inspected substrate.Specifically, the illumination optical system 30 is a telecentricoptical system with respect to the wafer 10 side. The optical axis O1 ofthe illumination optical system 30 is at an angle θ with respect to thenormal A1 to the stage 20.

In the illumination optical system 30 described above, the light fromthe illumination apparatus 60 is converted to p-polarized linearlypolarized light L via the first polarizing plate 32 and the first lens33, and is incident as illumination light on the entire surface of thewafer 10. Since the propagation direction (direction of the principalray of the linearly polarized light L reaching any point on the surfaceof the wafer 10) of the linearly polarized light at this time issubstantially parallel to the optical axis O1, the incident angle of thelinearly polarized light L is the same at each point of the wafer 10,since the light is a parallel luminous flux, and the incident anglecorresponds to the angle θ between the optical axis O1 and the normalA1.

In the present embodiment, since the linearly polarized light L incidenton the wafer 10 is p-polarized light, in a case in which the repetitiondirection of the repeating pattern 12 is set to an angle of 45° withrespect to the incident plane (propagation direction of the linearlypolarized light L at the surface of the wafer 10) of the linearlypolarized light L as shown in FIG. 4, for example, the angle formed bythe repetition direction of the repeating pattern 12 and the oscillationdirection of the linearly polarized light L at the surface of the wafer10 is also set to 45°. In other words, the linearly polarized light L isincident on the repeating pattern 12 so as to traverse the repeatingpattern 12 at an angle in a state in which the oscillation direction ofthe linearly polarized light L at the surface of the wafer 10 is at a45° angle to the repetition direction of the repeating pattern 12.

As shown in FIG. 1, the imaging optical system 40 is composed of asecond lens 41, a second polarizing plate 42, and an imaging apparatus45, and is disposed so that the optical axis O2 thereof is at an angle θwith respect to the normal A1 through the center of the stage 20.Consequently, direct reflection light directly reflected by the surface(repeating pattern 12) of the wafer 10 propagates along the optical axisO2 of the imaging optical system 40. The second lens 41 collects thedirect reflection light toward the imaging apparatus 45, the directreflection light having been directly reflected by the surface of thewafer 10. The direct reflection light from the wafer 10 thereby reachesthe imaging surface of the imaging apparatus 45 via the second lens 41and the second polarizing plate 42, and an image of the wafer 10 isformed.

The second polarizing plate 42 is disposed on the optical path between asecond lens 41 and the imaging apparatus 45, the azimuth of thetransmission axis thereof (the polarization direction) can be rotatedabout the optical axis of the imaging optical system 40 by using arotary drive apparatus 43, and the azimuth of the transmission axis ofthe second polarizing plate 42 is set so as to be tilted at an angleabout 90° from the transmission axis of the first polarizing plate 32.Consequently, (substantially right-angled) polarization componentshaving an oscillation direction that is different from that of thelinearly polarized light L as part of the direct reflection light fromthe wafer 10 (repeating pattern 12) can be extracted by the secondpolarizing plate 42 and directed to the imaging apparatus 45. As aresult, a reflection image of the wafer 10 formed by (substantiallyright-angled) polarization components having an oscillation directionthat is different from that of the linearly polarized light L as part ofthe direct reflection light from the wafer 10 is formed on the imagingsurface of the imaging apparatus 45.

The imaging apparatus 45 is composed of a CCD picture device or thelike, for example, which photoelectrically converts the reflection imageof the wafer 10 formed on the imaging surface and outputs an imagesignal to the image-processing apparatus 50. The brightness or darknessof the reflection image of the wafer 10 is substantially proportional tothe signal intensity (luminance) of the polarization components detectedby the imaging apparatus 45, and varies in accordance with the shape ofthe repeating pattern 12. The reflection image of the wafer 10 isbrightest in a case in which the repeating pattern 12 is ideally shaped.

The image-processing apparatus 50 acquires the reflection image of thewafer 10 on the basis of the image signal outputted from the imagingapparatus 45. A reflection image of a good wafer is stored in advance inthe image-processing apparatus 50 for comparison. A good wafer is one inwhich the repeating pattern 12 is ideally formed or considered to be ofideal shape on the entire surface of the wafer. The luminanceinformation (signal intensity) of the reflection image of a good waferis therefore considered to exhibit the highest luminance value.

Consequently, when the image-processing apparatus 50 acquires thereflection image of the wafer 10 functioning as the inspected substrate,the image-processing apparatus 50 compares the luminance information(signal intensity) thereof with the luminance information (signalintensity) of the reflection image of the good wafer. A defect in therepeating pattern 12 is detected on the basis of the amount by which theluminance value of a dark location is reduced in the reflection image ofthe wafer 10. For example, a determination of “defective” is made whenthe luminance variation is greater than a predetermined threshold value(allowable value), and a determination of “normal” is made when theluminance variation is smaller than the threshold value. The result ofcomparing the luminance information (signal intensity) by theimage-processing apparatus 50 and the reflection image of the wafer 10at that time are visibly displayed by a monitor unit of theimage-processing apparatus 50. The control apparatus 55 controlsoperations in general for the stage 20, the illumination apparatus 60,the rotary drive apparatus 43 of the second polarizing plate 42, theimage-processing apparatus 50, and other components.

The image-processing apparatus 50 may be configured so as to store areflection image of a good wafer in advance, as described above, or maybe configured so as to store a luminance threshold value and arrangementdata for a shot region of the wafer 10. In this case, the position ofeach shot region in the acquired reflection image of the wafer 10 isknown based on the arrangement data of the shot regions, and theluminance value of each shot region can therefore be calculated. Defectsin the pattern are then detected by comparing the luminance value withthe stored threshold value. A shot region in which the luminance valueis smaller than the threshold value triggers a determination of“defective.”

A surface inspection method using the surface inspection apparatus 1configured as described above will be described with reference to theflowcharts shown in FIGS. 6 and 7. The step of generating a referenceimage of a good wafer (not shown) performed at the time of recipecreation will first be described using the flowchart shown in FIG. 6.First, in step S101, a good wafer is conveyed onto the stage 20 andpositioned with respect to the repeating pattern on the good wafer. Thecontrol apparatus 55 at this time controls driving of the stage 20 sothat the azimuth angle (angle formed by the oscillation direction of thelinearly polarized light L on the surface of the wafer and therepetition direction of the repeating pattern) of the pattern withrespect to the oscillation direction of the linearly polarized light Lmatches the predetermined azimuth angle (of the initial setting). Thecontrol apparatus 55 also controls driving of the rotary drive apparatus43 at this time so that the bearing of the transmission axis of thesecond polarizing plate 42 with respect to the transmission axis of thefirst polarizing plate 32 is at the predetermined angle of inclination(of the initial setting). Also at this time, the control apparatus 55controls the operation of the first through third shutters 69 a through69 c so that the wavelength of the light emitted from the illuminationapparatus 60 is a prescribed wavelength (of the initial setting).

When the inspection conditions have thus been set, the linearlypolarized light L is irradiated onto the surface of the good wafer, andan image of the good wafer is captured in the next step S102, the imagebeing formed by polarization components having an oscillation directionat substantially a right angle to the linearly polarized light L as partof the direct reflection light from the surface of the good wafer. Atthis time, the light emitted from the illumination apparatus 60 isconverted to p-polarized linearly polarized light L by the firstpolarizing plate 32, converted to a parallel luminous flux by the firstlens 33, and irradiated onto the surface of the good wafer. The directreflection light reflected by the surface of the good wafer is collectedby the second lens 41, and polarization components having an oscillationdirection at a substantially right angle to the linearly polarized lightL as part of the direct reflection light are extracted by the secondpolarizing plate 42 and directed onto the imaging surface of the imagingapparatus 45. The imaging apparatus 45 then photoelectrically convertsthe reflection image of the good wafer formed by the polarizationcomponents having an oscillation direction at substantially a rightangle to the linearly polarized light L as part of the direct reflectionlight, and outputs an image signal to the image-processing apparatus 50.

When the image signal is outputted to the image-processing apparatus 50from the imaging apparatus 45, in the next step S103, theimage-processing apparatus 50 acquires the reflection image of the goodwafer on the basis of the image signal outputted from the imagingapparatus 45 and stores image data of the good wafer in an internalmemory (not shown) of the image-processing apparatus 50.

In the next step S104, a determination is made as to whether the goodwafer was photographed under all the necessary inspection conditions. Ina case in which the determination is “No,” after step S105 is performed,steps S102 and S103 are repeated under the inspection conditions inwhich an image had not yet been captured. In a case in which thedetermination is “Yes,” the process proceeds to step S106.

The inspection conditions determined in step S104 are the threeparameters of the azimuth angle of the pattern, the angle of inclinationof the second polarizing plate 42, and the illumination wavelength.Specifically, an image of the good wafer is captured for each set ofinspection conditions made up of combinations of the three parameters.Therefore, processing takes place in step S105 whereby the controlapparatus 55 changes the setting of at least one of the three types ofparameters in the inspection conditions. At this time, any azimuth angleselected from, e.g., 45°, 67.5°, and 22.5° is set as the azimuth angleof the pattern. This is because the condition (azimuth angle) underwhich the detection sensitivity increases with respect to defocusingvaries according to the type of pattern (e.g., memory circuit pattern orlogic circuit pattern). Azimuth angles of 135°, 157.5°, and 112.5° maybe further added.

The inclination angle of the second polarizing plate 42 is set at a 0.5°pitch in a range of 90° (crossed Nicols state)±4°. This is because indefect inspection (PER inspection) of the type performed in the presentembodiment, although the detection sensitivity with respect todefocusing has been found to increase when the inclination angle of thesecond polarizing plate 42 is slightly offset from 90° (crossed Nicolsstate), the condition for increasing the detection sensitivity variesaccording to the semiconductor process. The illumination wavelength isset to any of 546 nm (e-line), 436 nm (g-line) and 405 nm (h-line). Thisis also for the reason that the condition for increasing the detectionsensitivity varies according to the semiconductor process. However,since unevenness due to interference with the base of the pattern canoccur at some illumination wavelengths, such illumination wavelengthconditions are excluded from the inspection conditions in advance. Sinceunevenness due to interference with the base of the pattern alsosometimes occurs under some conditions irrespective of the illuminationwavelength, conditions that produce such anomalies are also excluded.

The quantity of illumination light is also adjusted by the first throughthird neutral density filters 65 a through 65 c in each inspectioncondition so that the luminance value (signal intensity) of the portionused as a reference in the image of the good wafer captured in step S102is constant. At this time, the control apparatus 55 controls driving ofthe rotary drive apparatuses (not shown) of the first through thirdneutral density filters 65 a through 65 c so that the luminance value(signal intensity) of the portion used as a reference in the image ofthe good wafer is constant, or in other words, so that standardizationis obtained according to the luminance value (signal intensity) of theportion (repeating pattern) used as a reference in the image of the goodwafer. The gain in the image-processing apparatus 50 may also beadjusted instead of adjusting the quantity of light through the use ofthe first through third neutral density filters 65 a through 65 c.

In step S106, the good wafer which has been photographed under aplurality of inspection conditions is unloaded and recovered from thestage 20, and in the next step S107, the image-processing apparatus 50compares pixels in the same pixel position in the images of the goodwafer photographed under a plurality of conditions, extracts each of thepixels (of the inspection conditions) having the smallest luminancevalue (signal intensity), and sets the current luminance value (signalintensity) as the luminance value (true value) for the correspondingpixel position.

In the next step S108, the image-processing apparatus 50 generates asingle reference image by connecting the pixels having the smallestluminance values (signal intensities) on the basis of the luminancevalue (signal intensity) of each pixel set in step S107. A referenceimage of the time of wafer inspection is thereby generated as an imageof the good wafer, and the reference image of the good wafer is storedin the internal memory of the image-processing apparatus 50. In stepS108, in a case in which the process is changed, such as when thematerial of the resist film changes in the same type of pattern, thesame processing as in steps S101 through S107 is performed for a goodwafer exposed/developed by the new process, and additional study can beperformed for replacing pixels whose luminance values (true values) havebecome relatively brighter by comparison with the reference image of thegood wafer stored in the internal memory.

The flowchart shown in FIG. 7 will next be used to describe the processfor inspecting the wafer 10. First, in step S201, the wafer 10 as theinspected substrate is conveyed onto the stage 20 and positioned withrespect to the repeating pattern 12 on the wafer 10. The controlapparatus 55 at this time controls driving of the stage 20 so that theazimuth angle of the pattern matches the predetermined azimuth angle (ofthe initial setting), under the same conditions as in the case ofgenerating the reference image of the good wafer. The control apparatus55 also controls driving of the rotary drive apparatus 43 so that theinclination angle of the second polarizing plate 42 is at thepredetermined inclination angle (of the initial setting), and thecontrol apparatus 55 controls the operation of the first through thirdshutters 69 a through 69 c so that the illumination wavelength is thepredetermined wavelength (of the initial setting).

When the inspection conditions have thus been set, the linearlypolarized light L is irradiated onto the surface of the wafer 10, and animage of the wafer 10 is captured in the next step S202, the image beingformed by polarization components having an oscillation direction atsubstantially a right angle to the linearly polarized light L as part ofthe direct reflection light from the surface of the wafer 10. At thistime, the light emitted from the illumination apparatus 60 is convertedto p-polarized linearly polarized light L by the first polarizing plate32, converted to a parallel luminous flux by the first lens 33, andirradiated onto the surface of the wafer 10. The direct reflection lightreflected by the surface of the wafer 10 is collected by the second lens41, and polarization components having an oscillation direction at asubstantially right angle to the linearly polarized light L as part ofthe direct reflection light are extracted by the second polarizing plate42 and directed onto the imaging surface of the imaging apparatus 45.The imaging apparatus 45 then photoelectrically converts the reflectionimage of the wafer 10 formed by the polarization components having anoscillation direction at substantially a right angle to the linearlypolarized light L as part of the direct reflection light, and outputs animage signal to the image-processing apparatus 50.

When the image signal is outputted to the image-processing apparatus 50from the imaging apparatus 45, in the next step S203, theimage-processing apparatus 50 acquires the reflection image of the wafer10 on the basis of the image signal outputted from the imaging apparatus45 and stores image data of the wafer 10 in an internal memory (notshown) of the image-processing apparatus 50.

In the next step S204, a determination is made as to whether the wafer10 was photographed under all the necessary inspection conditions. In acase in which the determination is “No,” after step S205 is performed,steps S202 and S203 are repeated under the inspection conditions inwhich an image had not yet been captured. In a case in which thedetermination is “Yes,” the process proceeds to step S206.

The inspection conditions determined in step S204 are the same as thoseunder which the reference image of the good wafer was generated.Specifically, as many images of the wafer 10 are captured as the numberof inspection conditions that are the same as those of the case in whichthe reference image of the good wafer was generated. Therefore,processing takes place in step S205 whereby the control apparatus 55changes the setting of at least one of the three types of parameters(azimuth angle of the pattern, inclination angle of the secondpolarizing plate 42, and illumination wavelength) in the inspectionconditions. The quantity of illumination light is also adjusted by thefirst through third neutral density filters 65 a through 65 c under thesame conditions as when the reference image of the good wafer wasgenerated.

In step S206, the wafer 10 which has been photographed under a pluralityof inspection conditions is unloaded and recovered from the stage 20,and in the next step S207, the image-processing apparatus 50 comparespixels in the same pixel position in the images of the wafer 10photographed under a plurality of conditions, extracts each pixel (ofthe inspection conditions) having the smallest luminance value (signalintensity), and sets the current luminance value (signal intensity) asthe luminance value (true value) for the corresponding pixel position.

In the next step S208, the image-processing apparatus 50 generates asingle inspection image by connecting the pixels having the smallestluminance values (signal intensities) on the basis of the luminancevalue (signal intensity) of each pixel set in step S207. An inspectionimage of the wafer 10 is thereby generated, and the inspection image ofthe wafer 10 is stored in the internal memory of the image-processingapparatus 50.

In the next step S209, the image-processing apparatus 50 compares theluminance information (i.e., inspection information) of the inspectionimage of the wafer 10 generated in step S208 with the luminanceinformation (i.e., reference information) of the reference image of thegood wafer generated previously in step S108, and determines that adefect is present when the luminance variation exceeds a pre-setthreshold value. At this time, the result of comparing the luminanceinformation (signal intensity) by the image-processing apparatus 50 andthe reflection image (inspection image) of the wafer 10 at that time arevisibly displayed by a monitor unit of the image-processing apparatus50, and visual inspection is also made possible.

As a result, through the surface inspection apparatus 1 and surfaceinspection method of the present embodiment, since the luminanceinformation (signal intensity) of the image of the good wafer isconsidered to exhibit the highest luminance value in defect inspection(PER inspection) such as that of the present embodiment, highly accurateinspection at high speed and high detection sensitivity is made possibleby performing inspection on the basis of an inspection image of thewafer 10 generated by extracting for each pixel of the image having thesmallest luminance value (signal intensity) among the images of thewafer 10 photographed under a plurality of inspection conditions andconnecting the pixels having the smallest luminance value (signalintensity), rather than conducting inspections under all inspectionconditions. The luminance value in the reflection image of the wafer 10decreases as well in cases in which exposure was not performed at thecorrect dose amount, but the optimum conditions for detecting doseamount defects vary according to whether the dose amount is excessive orinadequate. Thus, even for defects of the same type, the optimumconditions for detecting defects vary according to the severity of thedefect. Through the present embodiment, however, since the wafer 10 isinspected based on an inspection image of the wafer 10 generated byconnecting pixels having the smallest luminance value (signal intensity)among the images of the wafer 10 photographed under a plurality ofinspection conditions, defects of different types or defects of the sametype with different severity can all be easily recognized from a singleinspection image, and inspection can be performed with high detectionsensitivity and high accuracy. Inspecting a wafer on the basis of asingle inspection image in this manner also shortens the imageprocessing time for detecting defects for each shot, thus enablinghigh-speed inspection.

By generating the reference image of the good wafer by the sameprocedure as the inspection image of the wafer 10 is generated,erroneous detection of defects can be prevented, and a more highlyaccurate inspection can be obtained. Since the resist film of the wafer10 decreases in thickness from the center of the wafer 10 outward, thedose amount sometimes varies according to the thickness of the resistfilm. In such cases, the line width or the like is sometimes increasedin order to prevent the pattern from collapsing at the outside of thewafer 10 where the resist film is relatively thin, and the luminancevalue used as a reference in the good wafer then varies for each shot.However, by generating the reference image of the good wafer by the sameprocedure as the inspection image of the wafer 10, since a referenceimage of the good wafer is generated in which the luminance value variesfor each shot, erroneous detection of defects can be prevented, and amore highly accurate inspection can be obtained.

In the embodiment described above, three types of parameters includingthe azimuth angle of the pattern, the inclination angle of the secondpolarizing plate 42, and the illumination wavelength are varied in theinspection conditions in photographing the wafer, but this configurationis not limiting; a configuration may be adopted in which the setting ofonly one (or two) of the three types of parameters is varied(specifically, inspection conditions may be used in which the setting ofany one (or two) of the parameters including the azimuth angle of thepattern, the inclination angle of the second polarizing plate 42, andthe illumination wavelength is varied).

In the embodiment described above, the second polarizing plate 42 isconfigured so that the bearing of the transmission axis can be rotatedabout the optical axis O2 of the imaging optical system 40 by using therotary drive apparatus 43, but this configuration is not limiting. Forexample, a configuration may be adopted in which a ½ λ plate 47 isprovided between the second lens 41 and the second polarizing plate 42,and the bearing of the slow axis of the ½ λ plate 47 is rotated aboutthe optical axis O2 by using a rotary drive apparatus 48, as shown inFIG. 8.

In the embodiment described above, 546 nm (e-line), 436 nm (g-line), and405 nm (h-line) are used as the illumination wavelengths, but thisconfiguration is not limiting; other wavelengths may also be used, suchas 365 nm (i-line) and 313 nm (j-line).

In the embodiment described above, the image-processing apparatus 50generates the inspection image of the wafer 10 and inspects for thepresence of defects in the repeating pattern 12 on the basis of thegenerated inspection image of the wafer 10, but this configuration isnot limiting; each of an image processing unit for generating aninspection image of the wafer 10, and an inspection unit for inspectingfor the presence of defects in the repeating pattern 12 may beseparately provided.

1. A surface inspection apparatus comprising: an illumination unit forirradiating linearly polarized light onto a surface of an inspectedsubstrate having a predetermined repeating pattern; an imaging unit forcapturing an image of the inspected substrate formed by polarizationcomponents having an oscillation direction that is different from thatof the linearly polarized light as part of the reflected light from thesurface of the inspected substrate irradiated by the linearly polarizedlight; a setting unit for setting a plurality of conditions in at leastone of an illumination condition in the illumination unit and an imagingcondition in the imaging unit; and an information processing unit forcalculating a signal intensity for each portion of each of a pluralityof images of the inspected substrate photographed by the imaging unitunder the plurality of inspection conditions, comparing the signalintensity of the same portions in the plurality of images of theinspected substrate, and generating inspection information of theinspected substrate from information of the portions having the smallestsignal intensity.
 2. The surface inspection apparatus according to claim1, wherein the signal intensity is a signal intensity standardizedaccording to the signal intensity from a normal repeating pattern. 3.The surface inspection apparatus according to claim 1, comprising adisplay unit for generating an inspection image on the basis of theinspection information generated by the information processing unit andvisibly displaying the inspection image.
 4. The surface inspectionapparatus according to claim 1, comprising an inspection unit forinspecting for the presence of a defect in the repeating pattern;wherein the inspection unit is configured so as to inspect for thepresence of a defect in the repeating pattern by comparing theinspection information and predetermined reference information; theillumination unit irradiates linearly polarized light onto a surface ofa reference substrate as a reference for the inspection under theplurality of inspection conditions, and the imaging unit captures animage of the reference substrate formed by polarization componentshaving an oscillation direction that is different from that of thelinearly polarized light as part of the reflected light from the surfaceof the reference substrate irradiated by the linearly polarized light;and the information processing unit calculates a signal intensity foreach portion of each of the plurality of images of the referencesubstrate photographed by the imaging unit under the plurality ofinspection conditions, compares the signal intensity of the sameportions in the plurality of images of the reference substrate, extractsa portion having the smallest signal intensity for each of the portions,and generates the reference information from information of theextracted portion.
 5. The surface inspection apparatus according toclaim 1, wherein the inspection condition set by the setting unit is anangle formed by the oscillation direction of the linearly polarizedlight and the oscillation direction of the polarization components. 6.The surface inspection apparatus according to claim 1, wherein theinspection condition set by the setting unit is an angle formed by therepetition direction of the repeating pattern and the oscillationdirection of the linearly polarized light on the surface of theinspected substrate.
 7. The surface inspection apparatus according toclaim 1, wherein the inspection condition set by the setting unit is thewavelength of the linearly polarized light.
 8. A surface inspectionmethod comprising: a first step of setting an inspection condition; asecond step of irradiating linearly polarized light to a surface of aninspected substrate having a predetermined repeating pattern; a thirdstep of capturing an image of the inspected substrate formed bypolarization components having an oscillation direction that isdifferent from that of the linearly polarized light as part of thereflected light from the surface of the inspected substrate irradiatedby the linearly polarized light; and a fourth step of calculating asignal intensity for each portion of each of a plurality of images ofthe inspected substrate photographed under the plurality of inspectionconditions in the third step, comparing the signal intensity of the sameportions in the plurality of images of the inspected substrate, andgenerating inspection information of the inspected substrate frominformation of the portions having the smallest signal intensity.
 9. Thesurface inspection method according to claim 8, comprising a fifth stepof generating an inspection image on the basis of the inspectioninformation generated in the fourth step and visibly displaying theinspection image.
 10. The surface inspection method according to claim8, comprising: a sixth step of inspecting for the presence of a defectin the repeating pattern on the basis of the inspection informationgenerated in the fourth step, the sixth step comprising inspecting forthe presence of a defect in the repeating pattern by comparing theinspection information and predetermined reference information; aseventh step of irradiating linearly polarized light onto a surface of areference substrate as a reference for the inspection under theplurality of inspection conditions; an eighth step of capturing an imageof the reference substrate formed by polarization components having anoscillation direction that is different from that of the linearlypolarized light as part of the reflected light from the surface of thereference substrate irradiated by the linearly polarized light under theplurality of inspection conditions; and a ninth step of calculating asignal intensity for each portion of each of the plurality of images ofthe reference substrate photographed under the plurality of inspectionconditions in the eighth step, comparing the signal intensity of thesame portions in the plurality of images of the reference substrate toextract the portions having the smallest signal intensity for each ofthe portions, and generating the reference information from informationof the extracted portions.
 11. The surface inspection method accordingto claim 8, wherein the inspection condition set in the first step is anangle formed by the oscillation direction of the linearly polarizedlight and the oscillation direction of the polarization components. 12.The surface inspection method according to claim 8, wherein theinspection condition set in the first step is an angle formed by therepetition direction of the repeating pattern and the oscillationdirection of the linearly polarized light on the surface of theinspected substrate.
 13. The surface inspection method according toclaim 8, wherein the inspection condition set in the first step is thewavelength of the linearly polarized light.